Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of the common general knowledge in the field.
Presently the number of people wishing to have their hair coloured has increased. In order to obtain a uniform colour over the hair, permanent hair colours are used more often than temporary and semi-permanent hair colours. These types of temporary and semi-permanent hair colour do not give any control to the consumer over the amount of colour deposited. Hence most people prefer the permanent hair colours.
There are several permanent hair colouring compositions which generally come in two parts: a dye solution and a developer solution. These are generally synthetic chemicals and have a damaging effect on the hair. Each colouring application causes damage to the hair, and that damage is cumulative. Use of these dyes can also cause allergenic reactions in some people in addition to damage to structure of hair fiber.
In view of the fact that it would be desirable to develop a hair colouring composition and method that minimizes the damage caused to hair by the colouring method, there have been several attempts to permanently colour hair using black colour that is generated by using tannin and an iron salt.
It is also known in literature to use a two step method as a hair darkening system ((EP0394930, Kao, 1990), (JP04208214, Seihou Kikaku K K, 1992) and (EP0327345, Beecham, 1989)).
It is also known to pre-treat hair with a ferrous salt at a pH 3-6, in order to make the subsequent step of bleaching hair with hydrogen peroxide less damaging to hair and less irritating to skin. This invention also deals with the subsequent dyeing of hair with a colourant such as tannic acid or gallic acid which would react with iron to give the colour.
IN222788 (Hindustan Unilever Limited, 2004) discloses a method of colouring keratinous fibers by contacting the keratinous fibers sequentially with a solution/suspension of a ferric salt at pH below 3 and a colour developer selected from hydrolysable tannin or its breakdown products or derivatives or a mixture thereof obtained from a natural or synthetic source, where the sequence of contact is in any order.
It has now been found that contacting the keratinous fibers with an iron salt at pH below 2 including a reducing agent significantly enhances delivery of iron and combining it with a buffer effective in the pH range 3-6 for not more than 360 minutes prior to application and in presence of a penetration enhancer enhances the colour development that is effected by the application of the hydrolysable tannin and/or its breakdown products or derivatives. We have thus identified a superior delivery system for enhancing colour development of keratinous fibers which has not been disclosed in any of the prior art.
It is an object of the present invention to develop a method of colouring keratinous fibers that enhances the colouring effect.
It is another object of the present invention to develop a novel, stable, safe and inexpensive method of colouring keratinous fibers that enhances the colouring effect.
It is yet another object of the present invention to provide a colouring system for implementing the colouring method by providing the various components and instructions to use in the form of a kit.